Belleville, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

234
FXUS63 KLSX 170327
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1027 PM CDT Sat May 16 2026

.KEY MESSAGES...

- Additional scattered thunderstorms are possible (20-30%) this
  afternoon and evening. The main risk is large hail and damaging
  winds.

- Additional thunderstorm chances return early this week with a
  more widespread severe weather threat possible along a slow
  moving cold front Monday night into Tuesday.


&&

.SHORT TERM...  (Through Late Sunday Night)
Issued at 112 PM CDT Sat May 16 2026

An upper level trough has moved onshore over the western CONUS,
with a surface low over the Central High Plains and a warm front
extending into Iowa. There was a secondary warm front/convergence
zone draped along the I-70 corridor this morning, and this is
what kicked off this morning`s storms. These storms have reinforced
a baroclinic zone across the CWA, with temps in the upper 60s
across our north and pushing 80 in our south.

As we move through the afternoon and into the evening, additional
thunderstorm development will be largely focused to the north and
west of the area, near the primary warm front. However, the above
baroclinic zone may serve as a secondary focus for convection this
afternoon, and a few of the most recent runs of the HRRR are hinting
at that possibility. Given the weak forcing along this feature and
lack of deep forcing, I don`t expect widespread convection, but a
few additional thunderstorms remain a possibility. If these storms
do develop, MUCAPE around 2,500 J/kg and effective bulk shear around
30 kts may allow few of these storms to become strong enough the
support large hail or damaging winds.

The stronger convection expected to develop near NW MO should
grow upscale and track to the ENE through the night. While
previous runs of high-res guidance has largely kept these storms
to our north, a few of the CAMs have begun pushing them a bit
further south into our area. These storms may also pose a marginal
threat for damaging winds and large hail as they diminish and
move across NE MO and west-central IL this evening.

Tomorrow, longwave troughing will amplify over the western CONUS,
reinforcing deep southwesterly flow over the Mid-Mississippi Valley.
Given the lack of any focused forcing for ascent, it appears likely
that we`ll see little to no precipitation and notably less cloud
coverage than today. The increased insolation, coupled with the
above deep southerly flow, should push temperatures quite a bit
higher tomorrow.

BSH

&&

.LONG TERM...  (Monday through Next Saturday)
Issued at 112 PM CDT Sat May 16 2026

A compact shortwave will eject from the western CONUS trough on
Monday, spurring cyclogenesis over the Central Plains. The resultant
forcing for ascent from central KS through Iowa and into the Great
Lakes will force another round of thunderstorms, largely to the north
and west of our forecast area. These areas will also feature strong
dynamics, which coupled with a very unstable airmass, will result
in scattered/numerous strong to severe thunderstorms. The atmosphere
will also be rather unstable over the Mid-Mississippi Valley, but
without any focused forcing, anything more than widely scattered
thunderstorms appear unlikely. Additionally, much more modest
wind shear on our CWA will limit storm organization and severe
potential. Our best chance for severe weather through Tuesday
morning will be tied to whether the storms that develop to our
northwest are able to grow upscale and persist as they advance
into our forecast area.


A cold front associated with Monday`s surface low is expected to
push through the region on Tuesday. Ahead of the front, instability
should build into the 1000-2000 J/kg range, which coupled with the
front, will result in the best chance for thunderstorms in the
extended forecast. While the SPC convective outlook continues to
highlight our area on Tuesday, I do see a couple of factors that may
limit the potential for severe thunderstorms. First of all, the best
deep layer dynamics are expected to remain well to the north of our
forecast area, limiting deep layer shear to around 30kts ahead of
the front. Secondly, it`s unclear how storms from Monday night and
Tuesday morning will unfold across the area and whether the
atmosphere can recover before the frontal passage. Even if we do
recover, the above wind shear would be only marginally supportive
for severe thunderstorms. With that, the 15% contour from SPC seems
appropriate, but I would not expect that to increase much, barring a
notable change in the models.

The above cold front should push the deep moisture our of our
region, with the vast majority of guidance keeping dewpoints below
60 through the end of the week. Persistent weak zonal flow aloft
may open the door for a few weak shortwaves to move through the
region, but the lack of moisture will keep precipitation chances
limited.

BSH

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1022 PM CDT Sat May 16 2026

VFR conditions are expected at I-70 corridor terminals through
the 06Z TAF period. However, showers and likely a few
thunderstorms will continue to impact UIN over the next few hours,
including the first hour or two of the 06Z TAF period. Lightning,
bursts of heavy rain (with visibility reductions), and occasional
gusty winds are the most likely hazards with this activity.
Afterward, VFR conditions are likely to develop here as well and
persist through the end of he period.

Breezy south winds will develop by mid to late morning tomorrow
and persist through the end of the period. Another round of
showers and thunderstorms will likely move through the area just
beyond the end of the period Monday morning, but this is not yet
within the 06Z TAF window.

BRC

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX